Ion binding in sulfonate‐containing polyelectrolytes

Emf measurements have been used to study the activity and the extent of sodium ion binding to several polyelectrolytes, poly(styrenesulfonate) (PSS), poly(2‐acrylamido‐2‐methylpropanesulfonate) (PAMS), poly(3‐methacryloyloxypropane‐1‐sulfonate) (PMOS), and copoly[(N‐t‐butylacrylamide)‐(2‐acrylamido‐2‐methylpropanesulfonate)] (NB–AMS) (mole ratio 3.8:1). The activity coefficient of sodium ion in Na‐PAMS and Na‐PMOS without added salt is found to be in the range from 0.1 to 0.3 and is insensitive to changes in polymer concentration. However, it increases with increasing concentration of the added salt. The extent of sodium ion binding at a given sodium ion concentration, as estimated from the activity data for some sodium and tetrabutylammonium (TBA) salts, decreases in the order Na‐PAMS ≈︁ Na‐PMOS > TBA–PAMS > TBA–(NB–AMS). This indicates that a significant portion of the binding is attributed to the binding of TBA+ ions. Also compared are the results of ion binding in Na‐PAMS and Na‐PSS as a function of ionic strength. At low ionic strength (<1.0M), the order of binding strength is Na‐PAMS > Na‐PSS, while the order is reversed at high ionic strength (>1.0M). This finding is in good agreement with data obtained by dilatometry and viscometry.